1. Field of the invention
The present invention relates to an integrated circuit which may be internally configured by programming, for controlling the switching of a driving current through a single or multiple inductive loads connected across output terminals of the integrated device in accordance with one of several different connection schemes which may be selected for a particular application.
2. Description of the prior art
The controlled driving of stepping motors, transformers, electromagnets and similar actuating means, typically representing inductive loads, is commonly implemented by employing an integrated device combining the output power transistors, typically four power switching transistors connected to a virtual ground node which are referred to as "low-side drivers" and one or more often two power switching transistors connected to the supply rail, known as "high-side driver(s)", and a driving circuit. The latter typically includes a pulse-width-modulation (PWM) control loop, driven by a clock signal, which controls the "duty-cycle" of driving signals fed to the output power switching transistors in function of the detected value of the current flowing through the external load and of a control reference voltage.
Integrated circuits of this kind are well known to a skilled technician and may take different forms, more or less advantageous under certain aspects, but which essentially remain based upon PWM control loops. Among these types of circuits, particularly advantageous is a control circuit based upon a current sharing principle described in the pending U.S. patent application Ser. No. 07/245,657, filed on Sept. 16, 1988 and claiming a Convention priority date of Oct. 5, 1987, wherein by employing a single current sensing resistor for the current flowing through the external loads, it is possible to adjust independently the current flowing through two external loads connected according to a "dual-half-bridge" scheme or according to a "unipolar motor" connection scheme. The description of such a switching control circuit is here incorporated. On the other hand, the kind of the external inductive load or loads to be driven by the integrated circuit, whether represented by an unipolar motor or by one or more unidirectional motors, solenoids, and the like normally requires a specific design of the integrated switching control circuit compatible with the particular drive configuration or connection scheme of the external load or loads to be driven. In the accompanying FIGS. 1a, 1b, 1c and 1d, several well known driving schemes for inductive loads (L), according to a bridge, dual-half-bridge, electromagnet, and unipolar motor drive configuration are respectively depicted. In these illustrations six power switching transistors indicated with HSD1, HSD2 (that is the two High-Side Drivers), LSD1, LSD2, LSD3 and LSD4 (that is the four Low-Side Drivers), respectively, are shown, each being provided with a power diode for the recirculation of the discharge current of the relative external inductive load L. In case of driving an electromagnet, as depicted in FIG. 1c, the integrated circuit may contain also two additional recirculation diodes D1 and D2 as it is well known to a skilled technician. In all the examples shown, a single sensing resistor (Rsense), connected between a virtual ground node and the real ground of the supply circuit, is shown. Obviously the use of a single sensing resistor in the case of the circuit of FIG. 1b, that is a dual-half-bridge drive configuration for two external loads L and L', necessarily requires a current sharing kind of switching control circuit when an individual control of the two loads is desired, as described in the above cited application.
According to the prior art, the integrated circuit for controlling the switching must essentially be designed specifically for the contemplated application, for example a bridge type application (FIG. 1a), a unipolar motor application (FIG. 1d), and so forth.
Therefore it would be of great utility to provide an integrated device for controlling the switching of a drive current across external inductive loads (single or multiple loads), which could be internally configured so as to be usable for a driving scheme selectable among a number of possible driving schemes of the externally connected load or loads.